Banjo tablature stem length for beamed stems?

[address@hidden]

I’m working on some banjo tablature and I’d like to change the stem length for 
beamed stems when 2 non-adjacent strings are played together. I can use 
\override-s to lengthen and shift the stems of unbeamed notes. How can I change 
the length of beamed stems? It seems like beamed-lengths might hold the answer, 
but I haven’t figured out how to apply it or what the numbers mean. See the 
minimal example below. 
Thanks,
Holland 

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\version "2.18.0"

\new TabStaff {
        \set TabStaff.instrumentName = "Banjo"
        \set TabStaff.tablatureFormat = #fret-number-tablature-format-banjo 
        \set TabStaff.stringTunings = #banjo-open-g-tuning %gDGBD
        \tabFullNotation
        \numericTimeSignature
        \clef moderntab
         \relative c'   {       
\time 4/4
        
g8   < g'\5 d >8 
%how can I make this stem longer, like the unbeamed stem after it?
               r2.     |       
               
g,8  

 \once \override Stem.length = #12 % make the stem longer
  \once     \override Stem.Y-offset = #7 % moves the stem up
  \once \override Stem.Y-extent = #'(-7.0 . 0.0)
%moves the flag to the end of the moved stem

              < g'\5 d >8 

        
  } % end of banjo notes
  } % end of banjo voice